Support configuring HTTP2 for Tomcat 8.5 and 9

Description

within the Connector element, add a new HttpUpgradeProtocol element with className attribute set to org.apache.coyote.http2.Http2Protocol

for HTTP/2 over TLS in Java 8:

within the Connector element, when using NIO or NIO2 connectors, add a new sslImplementationName attribute set to org.apache.tomcat.util.net.openssl.OpenSSLImplementation (this is enabled by default when using APR connectors)

Optionally:

add the ability to select which kind of Connector protocol implementation will be used. If the default appears to work, then this won't be necessary.

Note that all modern browsers only support HTTP/2 over TLS today, so that is the preferred